Internal combustion engines employ spark plugs for igniting the air and fuel mixture in the engine cylinder combustion chamber for providing the power to rotate the crank shaft. Heretofore, spark plugs are provided with electrodes located outside the bottom end of the spark plug body to extend into the engine combustion chamber. In operation, the electrodes are exposed to the extremely high heat produced in the combustion chamber, which causes physical erosion of the electrodes. Also, burned particles such as carbon are deposited on the electrodes to result in the loss of effectiveness of the ignition function of the spark plug. Approximately, 80% of the air and fuel mixture is burned in each cycle of the ignition of a conventional spark plug. A large amount of waste materials including noxious gases such as carbon monoxide, carbon dioxide, nitrogen oxides and hydrocarbon and other partially burned or unburned materials are produced in the engine chamber in the ignition. Some of the materials and noxious gases are discharged from the engine to the atmosphere, which cause pollution of the latter. The pollution may be reduced by passing the discharge through a catalytic converter. However, the remaining waste materials in the ignition chamber will mix with the fresh air and fuel mixture subsequently injected into the ignition chamber to form a contaminated and degraded fuel mixture which inherent causes the reduction of the ignition efficiency and the loss of power output from the engine with high consumption of fuel. Furthermore, with the electrodes of the spark plug located in the combustion chamber, ignition would occurs in the combustion chamber of the engine so that the component parts in the combustion chamber are subjected directly to the high temperature of the combustion. The high temperature reduces the life of the engine due to heat stress of the components.
Attempts have been made to provide new spark plug constructions with the electrodes located within a hollow pre-ignition chamber formed in the spark plug body or shell surrounding the electrodes in a spaced manner. The central electrode and the grounding electrode are recessed and spaced from the lower opening of the pre-ignition chamber. The grounding electrode may also separate the pre-ignition chamber into a lower chamber between the central electrode and the lower opening of the shell and an upper chamber surrounding the insulated portion of the central electrode. Ignition occurs in the lower chamber so that the flame is injected into the cylinder chamber to ignite the air and fuel mixture therein resulting in less waste materials produced in the ignition and less high temperature exposure to the engine components. However, waste materials still produced in the pre-ignition chamber. The waste materials, again as in the conventional spark plug, would mix with the fresh air and fuel mixture injected into the cylinder chamber to form a concentrated polluted mixture in the pre-ignition chamber to cause unsatisfactory ignition and back fire.